The present invention relates to a liquid crystal data display device, and especially, to a TFT liquid crystal data display device or a PALC display device and the like.
The liquid crystal data display device represented by the liquid crystal display is being widely spread to the PC monitor market and the television market with its advantages as a thin, low-power-consumption display, along with the advance in technologies enabling the display to provide a high-speed-movement picture on a full-color wide screen.
One typical liquid crystal display is a transmission-type TFT liquid crystal display, the outline of which is now explained with reference to FIGS. 16, 17 and 18. As shown in FIG. 16, the TFT liquid crystal display comprises a color filter comprising pixels 11 including red, green, blue, and black masks, and a common electrode 12, a TFT substrate including a drive electrode 13 and a thin-film transistor 14 for applying voltage and thereby driving the liquid crystal, and a liquid crystal material 15 injected between the TFT substrate and the color filter. Moreover, polarizing plates 16 are placed on the front and back sides of the panel, and the shutter function of liquid crystal material 15 transmits or blocks light. Further, as shown in the cross-sectional view of FIG. 17 (a), a backlight unit 18 radiates light evenly on the whole surface of the liquid crystal panel 17. FIGS. 17 (b) and 17 (c) are the back view and the side view of FIG. 17 (a). The liquid panel 17 is mounted in a body 19 together with the backlight unit 18, thereby forming the liquid crystal display.
Next, the operation of the TFT is explained. Similar to a general transistor, the TFT comprises a source S, a gate G and a drain D. At the OFF state, as shown in FIG. 18 (a), no voltage is applied to the liquid crystal, and at the ON state, as shown in FIG. 18 (b), voltage VG is applied between the gate/drain of the liquid crystal.
Moreover, an edge (or side) type light or a subjacent (directly below) type light is known as the backlight unit. The edge light type is used mainly for office appliances (such as a laptop PC), and on the other hand, the subjacent type is mainly used for a mid- to small sized audiovisual equipment requiring higher brightness. Recently, there are greater demands for a more thinner, increased-brightness display, and improved fluorescent lamps and light conducting plates are being developed to match these demands, along with which the mid- to small sized audiovisual equipment are switched more from the subjacent type light to the edge-light type backlight unit. However, in a large-sized display of size 20 and larger, the subjacent-type light is more advantageous since the weight of the light conducting plate is too heavy.
Moreover, Japanese Patent Laid-Open Publication Nos. 11-73122 and 11-95215 disclose a liquid crystal data display device having an external light intake window and an optical detector, which is capable of varying the power to the backlight unit corresponding to the amount of external light, and to radiate light to the panel unit using both the backlight and the external light to improve the brightness while reducing power consumption of the display.
However, in the above-mentioned liquid crystal data display device, the brightness is not controlled actively corresponding to ambient illuminance. Moreover, there is a mechanism in some CRT devices to modify the brightness of the screen by controlling the strength of the image signals according to the ambient illuminance. However, in the case of a liquid crystal data display device, the light source and the image signals are controlled separately, so it was impossible to apply the same technique to the liquid crystal display.
Japanese Patent Laid-Open Publication Nos. 6-331962, 9-146073 and 10-170914 propose controlling the brightness of the back light in relation to the external light. The technology proposed in these publications are characterized in increasing the brightness of the backlight as the ambient illuminance increases, as shown in the characteristic curve 52 of FIG. 19. Further, Japanese Patent Laid-Open Publication No. 6-18880 proposes controlling the backlight to turn off when the ambient illuminance is sufficiently bright, as shown in the characteristic curve 53.
However, the former-mentioned prior art method had drawbacks in that the power consumption of the display is increased more and more, and the life of the backlight is thereby reduced. Moreover, according to the latter-mentioned prior art method, the power consumption is reduced if the ambient illuminance is sufficiently high, but when the backlight is turned off, the display suddenly became dark even when the illuminance is sufficient, making the display hard to see.
The present invention solves the problems of the prior art technology. The present invention aims at providing a liquid crystal data display device that is capable of providing appropriate brightness to the liquid crystal panel while reducing the power consumption thereof and improving the life of the backlight unit.
The present invention provides a liquid crystal data display device comprising a liquid crystal panel unit and a backlight unit, further comprising: an illuminometer for measuring ambient illuminance; and a means for computing panel brightness Bp (cd/m2) based on the following equation when the ambient illuminance is I (1x):
Bp=axc3x971n(I)+b 
wherein 10xe2x89xa6axe2x89xa640, and 50xe2x89xa6bxe2x89xa6250.
Moreover, the present invention provides a liquid crystal data display device, wherein the backlight unit is controlled so that the panel brightness is set to the optimum value corresponding to the ambient illuminance.
Further, the present invention provides a liquid crystal data display device, wherein the backlight unit is controlled so that the panel brightness is adjusted stepwise to the optimum value corresponding to the ambient illuminance.
Even further, the present invention provides a liquid crystal data display device further comprising when the panel brightness is represented by Bp (cd/m2) and the ambient illuminance is represented by I (1x), a means for classifying I into 1xe2x89xa6I less than 100, 100xe2x89xa6I less than 1,000, 1,000xe2x89xa6I less than 10,000, and 10,000xe2x89xa6I less than 100,000 (1x); computing the Bp value at both end points (start point and end point) of each class by Bp=axc3x971n (I)+b, wherein 10xe2x89xa6axe2x89xa640 and 50xe2x89xa6bxe2x89xa6250; and computing the average value of these values to obtain the Bp value of each class.
The present invention provides a liquid crystal data display device further equipped with a function for controlling the backlight unit so as to obtain a fixed panel brightness, and a function for controlling said backlight unit so that the panel brightness is set to the optimum value corresponding to the ambient illuminance, the device comprising a switch for selecting these two functions.
Moreover, the present invention provides a liquid crystal data display device further comprising a plural number of illuminometers, and a means for controlling the backlight unit so as to obtain a substantially uniform panel brightness throughout the screen.
Further, the present invention provides a liquid crystal data display device further comprising an external light intake window, and a means for controlling the backlight unit.
Even further, the present invention provides a liquid crystal data display device wherein the external light intake window is a prismatic light conducting plate.
Further, the present invention provides a liquid crystal data display device wherein the external light intake window is a half-mirror.
The present invention provides a liquid crystal data display device further comprising illuminometers mounted to the front surface and the back surface thereof for measuring the front-side ambient illuminance and the back-side ambient illuminance respectively, and a means for computing the panel brightness based on the front-surface ambient illuminance and controlling the backlight unit to obtain the desired panel brightness based on the back-surface ambient illuminance.
The present invention provides a liquid crystal data display device further comprising a plural number of liquid crystal panels, backlight units, the number of which is equal to or smaller than the number of the liquid crystal panels, and external light intake windows, the number of which is equal to or smaller than the number of the liquid crystal panels.
The operation according to the present invention will now be explained. According to the present invention, the relation of the ambient illuminance and the panel brightness is set as shown by the characteristic curve 51 of FIG. 19, wherein the panel brightness is controlled so as to increase logarithmically corresponding to the ambient illuminance. In other words, when the ambient illuminance is low (dark), the brightness of the backlight is increased logarithmically, so the brightness of the display is improved compared to the linear control offered by the prior art. Moreover, as the ambient illuminance increases, the brightness of the panel can be controlled to a soft brightness, which prevents the increase of power consumption of the backlight and improves the life of the backlight.